Examples of direct-current power supply devices include an insulated AC-DC converter which is structured by, for example, a diode bridge circuit that rectifies an alternating-current power supply, a DC-DC converter that steps down the direct-current voltage rectified in the diode bridge circuit to convert the voltage into a direct-current voltage with a desired potential and the like.
In a general insulated AC-DC converter, an X condenser is connected between AC terminals in order to attenuate the normal-mode noise and a discharging resistor is connected in parallel to the X condenser in order to quickly discharge the charges remaining in the X condenser when a plug is pulled out of an outlet.